This application claims the priority of British Application No. 0104508.7 filed Feb. 23, 2001, the disclosure of which is being incorporated herein by reference.
The present invention relates to a safety arrangement for a motor vehicle, and more particularly relates to a safety arrangement provided in association with a seat in the vehicle, which seat has an airbag mounted in front of it to provide protection for the occupant of the seat, and which seat may have a child safety seat mounted on it.
A large proportion of motor vehicles, such as motor cars, are provided with airbags to protect the occupants of the vehicle in the event that an accident should arise. For the front seat of a vehicle it is conventional to mount an airbag in the dashboard of the vehicle so that the airbag, when inflated in response to a sensed accident situation, is located in front of the occupant of the seat.
If a child seat is mounted on the front seat inflation of the airbag should be inhibited if the child seat is a rear facing child seat, and should, at least, be inflated in a less aggressive mode than normal if the child seat is a front facing child seat. The reason for this is that if the airbag inflates when a rear facing child seat is in position on the vehicle seat the inflating airbag will engage with the backrest of the child seat and will thus move the rear facing child seat towards the rear of the vehicle as the bag inflates. In some cases the occupant of the child seat may be ejected from the child seat by this sudden movement of the seat, and may even be thrown out of the rear window of the vehicle. If the child seat is forward facing the face of the occupant of the child seat will actually be quite close to the dashboard where the airbag is stored. If the airbag emerges from the dashboard in an aggressive manner it may physically strike and injure the occupant of the child seat.
It is quite normal to secure a child seat to an ordinary seat in a motor vehicle using the seat belt that is provided on a retractor mechanism in the vehicle for use by an ordinary occupant of the ordinary seat. A normal retractor which may be termed an ELR (Emergency Locking Retractor), is such that the belt can be freely withdrawn from and wound back onto the spool of the retractor unless an emergency situation is detectedxe2x80x94for example by detecting a predetermined acceleration of the vehicle or a predetermined speed of withdrawal of the belt from the retractorxe2x80x94in which case the retractor locks to prevent further safety belt being paid out. However, many retractors today are provided with a second mode of operationxe2x80x94the so-called ALR or Automatic Locking Retractor mode.
A retractor which has the ALR mode may operate in the same way as an ELR retractor until almost all of the belt has been paid out, and then the mode of operation will change so that, once the belt has been positioned, belt is blocked from being pulled out from the retractor, but may be pulled back into the retractor. Some forms of ALR retractor may be provided with a manually controllable switch to change the retractor from ELR mode to ALR mode. When a safety belt is used to mount a child seat in position, especially a rear facing child seat, virtually all of the belt should be withdrawn from the spool of the retractor so that if the appropriate type of ALR retractor is used the retractor enters the automatic locking mode. Thus, once the belt that secures the child in position has been located in the desired condition the retractor effectively locks to prevent further belt being withdrawn. Alternatively, the retractor may be manually switched to the ALR mode when the child seat has been mounted in position. It may be appropriate to manually switch to the ALR mode when mounting a forward facing child seat in position
It has been proposed (see DE-A-44 17 064) to use a control signal taken from an ALR retractor of a vehicle seat when it is in the automatic locking mode to inhibit or control the mode of operation of the airbag associated with the seat. Thus, when a child seat is mounted on the vehicle seat and the seat-belt is pulled almost fully out of the retractor, in an accident situation the airbag will not inflate, or will not fully inflate, thus reducing the risk that the airbag itself will cause injuries to the occupant of the child seat.
However, if an adult uses the seat which is provided with the airbag arrangement of DE-A-44 17 064 who is so large that the safety belt is pulled out of the retractor far enough to make the retractor enter the automatic locking mode, or if the retractor should be in the ALR mode for some other reason, then the mode of operation of the airbag will be controlled so that in an accident situation the airbag will not inflate, or will not fully inflate. This is very undesirable as the airbag will then not provide adequate protection for the occupant of the seat.
The present invention seeks to provide an improved safety arrangement.
According to this invention there is provided a safety arrangement for a motor vehicle, the arrangement including a seat for an occupant of the vehicle, an airbag, adapted to be inflated in an accident situation to provide protection for the occupant of the seat, the airbag having a first mode of operation and a second, less aggressive mode of operation, a safety-belt for use by the occupant of the seat, the safety-belt being provided with a retractor interchangeable between an ELR mode of operation and an ALR mode of operation, there being first means for determining whether the retractor is in the ALR mode, and second means for determining whether the down-force on the seat is less than a first threshold, which first and second means are associated with means which control the mode of deployment of the airbag during an accident situation, so that if the retractor is in the ALR mode of operation and if the down-force on the seat is less than the first threshold, the airbag is deployed in the second, less aggressive, mode of operation.
In one embodiment, in the second mode of operation, the airbag is not inflated at all. In an alternative embodiment, in the second mode of operation the airbag is only partially inflated, as compared with the first mode of operation. In the second mode of operation, the airbag is inflated relatively slowly, as compared with the first mode of operation.
In one embodiment the first threshold is approximately 60 kg.
Conveniently means are provided for determining if the down-force on the seat is lower than a second threshold, which is lower than the first threshold, and to cause the means which control the mode of deployment of the airbag to cause the airbag to be deployed in the second, less aggressive mode of operation if the down-force on the seat is less than said second threshold.
Preferably the second threshold is approximately 35 kg.
In one embodiment an output from the first means which determine whether the retractor is in the ALR mode, and the output of the second means that determine whether the down-force on the seat is less than a first threshold are passed to an AND gate, the output of which is passed to an OR gate, a second input to the OR gate being the output of the means for determining if the down-force on the seat is lower than the second threshold, the output of the OR gate being supplied to the means which control the mode of deployment of the airbag.
The first and the second thresholds may be predetermined thresholds, but in some embodiments the thresholds may be variable.